Integrated circuit data security devices are known in the art. For example, such data security devices are used by the U.S. Government to protect sensitive government information.
One known way to "break" a data security device is to provide a very slow externally-controlled system clock to the data security device. If the externally-provided clock is sufficiently slow, one may use integrated circuit probing techniques (such as E-beam probers) to determine the state of internal nodes of the data security device and, thus, determine the contents sensitive information that the data security device was designed to protect. For this reason, as a safeguard, conventional data security devices cannot be driven by an externally-controlled clock.
However, this safeguard makes the conventional data security device difficult to test since most (if not all) testers must control the clock signal of the integrated circuit that they are testing. That is, the tester is designed to provide all of the inputs to the integrated circuit, including the clock signal. After each pulse of the tester-provided clock signal, the tester looks for an expected pattern on the integrated circuit outputs. Thus, if the integrated circuit is not operable with an external clock, provided from a tester, resort must be had to non-conventional custom (thus expensive) testers.